Re: SEARCH and CYCLE clauses

Hi

pá 9. 10. 2020 v 12:17 odesílatel Pavel Stehule <pavel.stehule@gmail.com> napsal:

pá 9. 10. 2020 v 11:40 odesílatel Peter Eisentraut <peter.eisentraut@2ndquadrant.com> napsal:

On 2020-09-22 20:29, Pavel Stehule wrote:
> The result is correct. When I tried to use UNION instead UNION ALL, the
> pg crash

I fixed the crash, but UNION [DISTINCT] won't actually work here because
row/record types are not hashable.  I'm leaving the partial support in,
but I'm documenting it as currently not supported.

 

 I think so UNION is a common solution against the cycles. So missing support for this specific case is not a nice thing. How much work is needed for hashing rows. It should not be too much code.

> looks so clause USING in cycle detection is unsupported for DB2 and
> Oracle - the examples from these databases doesn't work on PG without
> modifications

Yeah, the path clause is actually not necessary from a user's
perspective, but it's required for internal bookkeeping.  We could
perhaps come up with a mechanism to make it invisible coming out of the
CTE (maybe give the CTE a target list internally), but that seems like a
separate project.

The attached patch fixes the issues you have reported (also the view
issue from the other email).  I have also moved the whole rewrite
support to a new file to not blow up rewriteHandler.c so much.

--
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

This patch is based on transformation CYCLE and SEARCH clauses to specific expressions - it is in agreement with ANSI SQL

There is not a problem with compilation

Nobody had objections in discussion

There are enough regress tests and documentation

check-world passed

doc build passed

I'll mark this patch as ready for committer

Possible enhancing for this feature (can be done in next steps)

1. support UNION DISTINCT

2. better compatibility with Oracle and DB2 (USING clause can be optional)

Regards

Pavel

Status update for a commitfest entry.
According to cfbot patch no longer applies. So I moved it to waiting on author.

-- 
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company